In order to carry out a gearshift, in automatic transmissions with hydraulically actuated shift elements having a shifting piston moving in a piston space and placed on a disc set, the piston space, which at first is more or less filled with air, must be filled with oil before the piston is finally placed on the disc set. Said filling and feeding operation of shift elements is usually divided into a rapid filling phase and a filling equalization phase. In the rapid filling phase the shift element that operates almost completely or partly idly is filled with oil, and in the subsequent filling equalization phase the shift piston is finally placed on the disc set with less load.
It is generally known from extensive empirical tests that the precision of said operation, especially with an exactly coordinated feeding pressure, has a very great influence upon the gearshift quality.
In the practice, in transmission coordination, it has repeatedly proven problematic that the coordination parameters of the filling operation (which are determined by necessary manufacturing tolerances) differ from one transmission to another. In addition, the coordination parameters of the filling operation are also time dependent since the tolerances change as result of aging and wear through time.
For example, in the rapid filling phase, which fills the piston space (operating idly or partly idly) with oil, the necessary tolerance of the air play determined by the manufacture, that is, the path of the shift piston to the discs, together with the manufacturing tolerance, is to be regarded as a variance. If the air play increases, for example, as a consequence of disc wear, the duration of the filling phase must be extended in order to cover the additional need of oil and to exactly carry out the feeding operation.
With the former processes known from the practice, it cannot be accomplished to the extent desired to give a uniform coordination to one type of transmission.
The necessary filling equalization pressure likewise depends on a series of parameters. Thus, when using plate springs, for example, with increasing rigidity and increasing piston friction, the filling equalization pressure must be raised in order to place the shift piston exactly on the discs.
Divergences of pressure regulators also impair shifting quality, whereby a correction of the filling equalization pressure (corresponding to the divergences of pressure regulators) is required in order to bring the shift pistons, after the filing, to lie on the disc sets with a required slight load.
A uniform, single type transmission coordination thus necessarily results in gearshifts of reduced quality.
EP 0 435 377 discloses a process for regulating the change from a low velocity ratio to a high velocity ratio between the input and output shafts of an automatic transmission with shift elements, or a coupling and an uncoupling torque transmitting apparatus operated by fluid pressure. In a filling and feeding operation of the hydraulically actuated shift elements, the pressure curve is through time adapted to the transmission conditions by means of an adaptive diagram.
When the engine throttle is substantially closed, the uncoupling, torque transmitting apparatus is first disengaged by reducing its operating pressure prior to a change or modification. The coupling, torque transmitting apparatus is disengaged by applying a coupling instruction pressure for a previously defined filling period. The coupling instruction pressure, here adjusted to an initial value, is subsequently regulated in a close loop regulation period in order to effect a progressive engagement of the coupling, torque transmitting device. An increase in the coupling instruction pressure above a previously determined value during the regulation period, or a moderate filling of the coupling transmission apparatus, is detected by the measure of a velocity divergence. According to this detection either a first stored parameter, which relates to the value of the initial coupling instruction pressure, is adjusted in order to increase the initial coupling instruction pressure, or a second stored parameter, which relates to the length of the filling period, is adjusted in order to extend the filling period.
This process offers the advantage that the gearshift quality is analyzed and required adaptations regarding pressure and time in the filling period are calculated and made the basis of the subsequent gearshifts, whereby their quality is optimized.
However, this known process is disadvantageous in that a learning period is needed in all driving conditions in order to achieve an optimal operating condition. Consequently, in a new transmission, after a transmission change, or after transmission repairs, the gearshift quality is initially impaired when using said known coordination process.
In connection with this, EP 0 435 374 and EPO 0 435 378 are to be cited also since their adaptation processes also have the disadvantage that the parameter optimization acts upon the process only with definite delay due to the needed learning process.
Therefore, the invention is based on the problem of providing a process of the above mentioned kind in which the separate shift elements for each transmission are filled from the beginning using optimal parameters in order to ensure an optimal operating quality.